FIG. 1 is a diagram illustrating a network structure of a universal mobile telecommunication system (UMTS). Generally, a UMTS system 10 comprises a user equipment (UE) 11, a UMTS terrestrial radio access network (UTRAN) 12, and a core network (CN) 13. Herein, the UE may be a mobile terminal in general. The UTRAN 12 comprises at least one of radio network sub-systems (RNSs) 13, and each RNS comprises a radio network controller (RNC) 131 and at least one of Node B 132 which is controlled by the RNC. The Node B includes at least one cell 133.
FIG. 2 is a diagram illustrating a layer structure of radio interface protocol in mobile communication system. As shown in FIG. 2, the radio interface protocol comprises horizontally a physical layer, a data link layer and a network layer. Meanwhile, the radio interface protocol comprises vertically a user plane for transmitting user data and a control plane for signaling.
The protocol layers of FIG. 2 comprises L1 (the first layer), L2 (the second layer) and L3 (the third layer). The layers of FIG. 2 correspond to 3 layers from the bottom according to the open system interconnection (OSI) layer structure.
The first layer, i.e., the physical (PHY) layer, provides the higher layer with information transfer service through physical channels. The PHY layer is connected to the second layer, i.e., medium access control (MAC) layer, with transport channels and data is transferred between MAC layer and PHY layer through the transport channels. Meanwhile, data is transferred between the PHY layers of a transmitting side and the PHY layer of a receiving side through the PHY channels.
The MAC layer provides a radio link control (RLC) layer with service through logical channels. The RLC layer of L2 supports reliable data transmission and may segment and concatenate service data units (SDUs) transferred from a higher layer.
A radio resource control (RRC) layer located at the bottom of L3 in the protocol layers is defined on the control plane, may control the logical channels, the transport channels and the physical channels in relation to configuration, reconfiguration and release of radio bearers (RBs). Herein, the RB means a service supported by L2 for data transmission between UE and UTRAN. Generally, to set up a RB means a process for defining a protocol layers and channels for providing a specific service, as well as a process for configuring parameters and operation, corresponding to the specific service.
Moreover, the RRC layer may broadcast system information through a broad control channel (BCCH). The system information regarding a cell is broadcasted to UEs using at least one of system information block (SIB). If the system information is modified, the UTRAN transmits BCCH modification information to the UEs through a paging channel (PCH) or a forward access channel (FACH), for the UEs to have the latest system information.
As an example of point-to-multipoint service, multimedia broadcast/multicast service (MBMS) is explained as follows. The MBMS supplies a streaming or background service using a MBMS bearer which is set up generally for downlink transmission. A MBMS service comprises at least one session, MBMS data is transmitted to UEs using the MBMS bearer during ongoing session. If the UE is activated corresponding to a service to which the UE have been subscribed, the UE may receive the service.
FIG. 3 is a diagram illustrating channels for MBMS. The UTRAN provides UEs with MBMS using a RB. The UTRAN may set up two types of RBs, i.e., a point-to-point RB and a point-to-multipoint RB. Herein, the point-to-point RB corresponds to a bi-directional RB. The point-to-point RB employs a dedicated traffic channel (DTCH) as a logical channel, a dedicated channel (DCH) as a transport channel, and a dedicated physical channel (DPCH) or a secondary common control physical channel (SCCPCH) as a physical channel.
Meanwhile, the point-to-multipoint RB corresponds to a uni-directional RB. As shown in FIG. 3, the point-to-multipoint RB may employ the MBMS traffic channel (MTCH) as a logical channel, the FACH as a transport channel, and the SCCPCH as a physical channel. The MTCH is configured for each MBMS provided in a cell, is used for transmission of user data corresponding to a MBMS on the user plane. A MBMS control channel (MCCH) which is a logical channel is mapped to the FACH, and the transport channel FACH is mapped to the SCCPCH. In general, one MCCH is allocated to one cell.
According to the related art, if the SCCPCH to which the MCCH is mapped is reconfigured, the UTRAN transmits control information through both the previously configured SCCPCH and the reconfigured SCCPCH for a while, because the UE isn't aware of the timing of SSCPCH reconfiguration. Therefore, the transmission of the control information through two physical channels causes waste of radio resource.